Is Pyrex Resistant to Molten Lye?

[Theophrastus]

See the above.

[hermanntrude]

probably not.

 

don't mess with that stuff. Also, IUPAC names are the new thing. try them. people might know what you're talking about more often.

[Theophrastus]

Out of sheer interest, what containers are then? I was thinking of using molten sodium hydroxide to get a good yield of terephthalic acid, but I suppose I'll use an alcohol solvent instead, or perhaps even settle with water; though I've heard the yield's pretty pitiful. (FYI I thought of adding polyethylene terephthalate to molten sodium hydroxide, to get ethylene glycol (which I can condense, and use as a precursor for making formalin) and sodium terephthalate. The sodium terephthalate I would then via hydrochloric acid, convert to terephthalic acid (and sodium chloride), which I could then use to make benzene. Joy.

 

And the whole lye- sodium hydroxide thing's common knowledge; I just like the sound of lye better. It just sounds so wonderfully sinister ...

 

[edit]

 

Damn, have I really been away for so long so as to forget Hazmat? Ah yes, let's see, molten lye can eat through human tissue with ease (among other things). Hydrochloric acid can also be dangerous, and one should only handle it with the necessary safety precautions; goggles, chemical- resistant gloves and some manner of external bodily protection (like a lab coat). Ah, and formalin (or aqueous formaldehyde) is extraordinarily toxic; even small dosages, can be lethal.

Edited September 17, 2009 by Theophrastus

[UC]

No, any silica glass (including fused quartz) or silicate ceramic will be attacked by molten lye. Stainless steel vessels are good for molten lye, but not if oxidizers are to be included. I recommend a cast iron crucible in this case, as a protective layer of magnetite should be formed.

 

Molten lye with nothing added is surprisingly tame, but you need some serious protection if you want to add anything that may cause splashes or spatters.

[Theophrastus]

Thanks UC, I'll go buy a stainless steal pot for this one (or something of the sort). And no, there won't be any splashes. The only thing I'm worried about is ethylene glycol vapour, which boils before sodium hydroxide melts. I thought of using an alcohol- based solent, as it would be a lot safer, but I don't think the yield would be as good. I could try and plug any possible holes, but I'm worried of what'll occur if the ethylene glycol escapes. Of course I will be reared incapable of seeing what is going on, but it's just safer that way. I guess I'll probably run it for about 15 minutes, then leave it for an hour to cool, in an ice bath. Joy.

 

Any thoughts? Concerns? Reasons to cry?

[UC]

Thanks UC, I'll go buy a stainless steal pot for this one (or something of the sort). And no, there won't be any splashes. The only thing I'm worried about is ethylene glycol vapour, which boils before sodium hydroxide melts. I thought of using an alcohol- based solent, as it would be a lot safer, but I don't think the yield would be as good. I could try and plug any possible holes, but I'm worried of what'll occur if the ethylene glycol escapes. Of course I will be reared incapable of seeing what is going on, but it's just safer that way. I guess I'll probably run it for about 15 minutes, then leave it for an hour to cool, in an ice bath. Joy.

 

Any thoughts? Concerns? Reasons to cry?

 

Is this decomposing PETE plastic? It'll work better with some water in the mix and ethylene glycol or diethylene glycol solvent, trust me. If you fuse with lye, it'll make benzene instead.

[Theophrastus]

Thanks, yeah that's it exactly. Thanks for the note; at least I know it would be a hell of a lot easier (no molten lye, and therefore ethylene glycol vapours), but like I said, I don't have any ethylene glycol as it is, (I was actually planning to use the batch I make to either convert to formaldehyde, or glyoxal) so I guess I'll use a solution of ethanol and water, and see how it turns out. I was actually planning to then try to electrolytically decompose the terephthalic acid (I'd add hydrochloric acid to the sodium terephthalate formed, and the terephthalic acid is nearly insoluble in water and ethanol) to make benzene, which for me would be a hell of a lot cheaper and easier, than buying it. Yay synthesis!

[John Cuthber]

Just a thought.

Do you plan to make the terphthalic acid into benzene by heating it with a strong alkali to decarboxylate it?

If so, how do you plan to ask it not to decarboxylate the first time you heat it with molten NaOH? (I think that's what UC meant)

 

I know that there's Kolbe's method for turning acids into hydrocarbons but unless it does some clever trick, the expected product from terphthalic acid would be some biphenyl derivative.

http://en.wikipedia.org/wiki/Kolbe_electrolysis

[Theophrastus]

Well the molten lye thing's out of the picture, so no worries John. And yes, I was thinking of something on the lines of Kolbe Electrolytic Synthesis, but you raise a very good point (Yay you!); I could instead decarboxylate the terephthalic acid later formed, with molten lye, rather than winding up with naphthalene, and other unwanted biproducts, via the Kolbe electrolytic synthesis. (Not fun.)

 

However, if I do try out this method, it'll only be in a while, as I'm still in the process of making a new condenser/still for refining alcohols, benzene and whatnot, and benzene has a rather low boiling point (or at least certainly lower than sodium hydroxide).

 

ps: I've started the experiment, with 150mL of 50% ethanol, and have added some sodium hydroxide and PETE flakes. I'll run the solution for about a day, then post the results. When I'm done, I'ld add some HCl, and see what my terephthalic acid yield was. Happy experimenting!

 

-Theo

[UC]

Well the molten lye thing's out of the picture, so no worries John. And yes, I was thinking of something on the lines of Kolbe Electrolytic Synthesis, but you raise a very good point (Yay you!); I could instead decarboxylate the terephthalic acid later formed, with molten lye, rather than winding up with naphthalene, and other unwanted biproducts, via the Kolbe electrolytic synthesis. (Not fun.)

 

However, if I do try out this method, it'll only be in a while, as I'm still in the process of making a new condenser/still for refining alcohols, benzene and whatnot, and benzene has a rather low boiling point (or at least certainly lower than sodium hydroxide).

 

ps: I've started the experiment, with 150mL of 50% ethanol, and have added some sodium hydroxide and PETE flakes. I'll run the solution for about a day, then post the results. When I'm done, I'ld add some HCl, and see what my terephthalic acid yield was. Happy experimenting!

 

-Theo

 

You may need a few weeks to accomplish the reaction in aqueous ethanol. It can even be done without the alcohol, but takes longer still.

 

The main point of the ethylene glycol is that you can heat it strongly, which speeds up the reaction.

[Theophrastus]

Alright, a week it is then. I suppose I might as well take the time to add some more sodium hydroxide and PETE, if it's gonna sit that long. I'll be leaving town on Tuesday, and returning the next weekend, so that'll be ample time for the reaction. Let's see what happens.

[Theophrastus]

Well, school work's kept me back for some time, but I've finally managed to respond. The experiment itself went rather successfully, and by the end of the week, the solution had turned a lovely yellowish- golden colour (due to the dissolved sodium terephthalate) with insoluble plastic materials (whose size had greatly decreased due to reaction) and small amounts of undissolved sodium terephthalate at the bottom.

 

I then proceeded to empty out my initial 250ml flask, into a larger erlenmeyer flask (a little over 500ml), and added water, dissolving the remaining sodium terephthalate. (I actually accidentally went a little too far, and wound up diluting it a fair bit (thus the more bland colour of the solution in my second picture). I then filtered the solution, the filtration process being rather slow towards the end, taking about half an hour.

 

I have yet to actually add the hydrochloric acid to precipitate the terephthalic acid, but will do so when I have some more free time. I was thinking of purifying my leftover ethylene glycol solution, after that, but it would have to be done outside, due to the dioxane formed.

 

A tad unrelated, but how would one go about making high purity dioxane from ethylene glycol. (Relax, I know dioxane is nasty stuff and that in many cases, there are numerous ethers that are far safer and equally efficient in solvation. It's more of an out- of- interest thing than anything else.)

 

ps: I've posted the photos of this synthesis on my profile.

[UC]

Well, school work's kept me back for some time, but I've finally managed to respond. The experiment itself went rather successfully, and by the end of the week, the solution had turned a lovely yellowish- golden colour (due to the dissolved sodium terephthalate) with insoluble plastic materials (whose size had greatly decreased due to reaction) and small amounts of undissolved sodium terephthalate at the bottom.

 

I then proceeded to empty out my initial 250ml flask, into a larger erlenmeyer flask (a little over 500ml), and added water, dissolving the remaining sodium terephthalate. (I actually accidentally went a little too far, and wound up diluting it a fair bit (thus the more bland colour of the solution in my second picture). I then filtered the solution, the filtration process being rather slow towards the end, taking about half an hour.

 

I have yet to actually add the hydrochloric acid to precipitate the terephthalic acid, but will do so when I have some more free time. I was thinking of purifying my leftover ethylene glycol solution, after that, but it would have to be done outside, due to the dioxane formed.

 

A tad unrelated, but how would one go about making high purity dioxane from ethylene glycol. (Relax, I know dioxane is nasty stuff and that in many cases, there are numerous ethers that are far safer and equally efficient in solvation. It's more of an out- of- interest thing than anything else.)

 

ps: I've posted the photos of this synthesis on my profile.

 

Use a different acid. You risk making bis-(2-chloroethyl)ether if there is any diethylene glycol contaminant around. This is an analogue of sulfur mustards, and while not nearly as nasty, is still nothing you want to be dealing with.

 

Dioxane is probably better made from diethylene glycol, by reaction with hot sulfuric acid, with continuous distillation of the product, analagous to the production of diethyl ether.

[sivas54]

Molten lye means hot concnetrated NaOH solution(>30% if from membrane cell or >50% if produced from Mercury cell). It attacks pyrex glass, even MS tanks. container made of Nickel and INCONEL can be used for handling caustic lye

[hermanntrude]

Molten lye means hot concnetrated NaOH solution(>30% if from membrane cell or >50% if produced from Mercury cell). It attacks pyrex glass, even MS tanks. container made of Nickel and INCONEL can be used for handling caustic lye

 

molten lye means liquid sodium hydroxide (not aqueous). The question has already been answered anyway. Please read a thread before responding to it.

[sivas54]

Yes. I agree that "molten' is wrong. I apologise for not doing proper editing before placing the reply